This is pure conjecture but, Elisa is looking for a plea. But first she wants to lead the police on a wild goose chase to try to establish she only suspects Adam and knows nothing of the details of the crime.
To put doubt of her direct knowledge she is likely cooperating with police saying she only helped Adam cover up "what're it was he dun". There has been two "promising leads" that amounted for Jack shit. I got 20 on third time being a the charm.
Elisa is giving them possible locations to search. Not the knowledge she in fact possess which is going to be the dump site for the bed. She can't implicate herself beyond that. She will find the bed and MAYBE the leg. But you can be rest assured she will not give the location of the body (if one exists). In trial her defense can show she cooperated with police in the parts she new about. Covering up Adam's crime.
So knowing LE knows this and is playing along to get the goods, they got to enjoy a nice country drive to Caldwell County. A place known to Elisa as they lived there 3 years previously. A forest road towards Granite falls.The conversation in the truck was likely not related to the case but a lovely dialogue about the weather or favorite colors. It is common for a liar to use pieces of their past to build new truths.
So she gets to take a ride and then return to her sell another piece of the puzzle added. Once LE puts in the last few pieces they will expose these pieces were not from this puzzle at all.
I just can't help but feel like at this point the sheriff's office is along for the ride. I really hope I am right that they know this game and nail this woman to the wall.